Treatment of an aqueous waste stream from a hydrocarbon conversion plant with continuous recycle of the treated aqueous stream



Sept. 22, 1970 p, U N ETAL 3,530,0fi3

TREATMENT OF AN AQUEOUS WASTE STREAM FROM A HYDROCARBON CONVERSION PLANTWITH CONTINUOUS RECYCLE OF THE TREATED AQUEOUS STREAM Filed Sept. 16.1968 Separating Zone 1 a Q 7* g 1 a E N g E N m 3 E m g ii "I A TTORNEYSUnited States Patent Ofiice 3,530,003 Patented Sept. 22, 1970 US. Cl.208-108 11 Claims ABSTRACT OF THE DISCLOSURE A hydrocarbon charge stockcontaining sulfurous and nitrogenous contaminants is converted andelemental sulfur and ammonia is simultaneously recovered by the stepsof: (a) contacting in a hydrocarbon conversion zone the hydrocarboncharge stock, hydrogen and an aqueous recycle stream containing .(NH S Owith a hydrocarbon conversion catalyst at conversion conditionssufficient to form an effluent stream containing substantiallysulfurfree and nitrogen-free hydrocarbons, hydrogen, NH H 8, and H (b)cooling and separating the efiluen-t stream from step (a) to form ahydrogen-rich gaseous stream, a hydrocarbon-rich liquid product stream,and an aqueous waste stream containing NH HS; (c) catalytically treatingthe aqueous waste stream from step (b) with oxygen at oxidizingconditions effective to produce an eflluent stream containing elementalsulfur or ammonium polysulfide, NH OH and (NH S O (d) separating sulfurand ammonia from the effiuent stream from step (c) to produce theaqueous recycle stream containing (NH S O and (e) passing this lastaqueous stream to step (a). Key feature of the resulting process is thecontinuous recycle of the treated water back to the hydrocarbonconversion process with consequential abatement of water pollutionproblems and substantial reduction of requirements for make-up water.

The subject of the present invention is a combination process directedtowards the catalytic conversion of a hydrocarbon charge stockcontaining sulfurous and nitrogenous contaminants with continuousrecovery of at least a portion of the sulfur and ammonia from theproduct of the hydrocarbon conversion reaction without causing anysubstantial water pollution problems. More precisely, the presentinvention relates to processes for the conversion of hydrocarbon chargestocks containing sulfurous and nitrogenous compounds wherein an aqueouswaste stream containing substantial quantities of NH; and H S (typicallypresent as NH HS) is produced and wherein this waste stream is treatedto recover elemental sulfur and ammonia and to produce a treated waterstream containing ammonium thiosulfate and it is desired to recycle thislast aqueous stream to the process in order to remove additionalquantities of NH and H 8, to abate a substantial pollution problem, andto minimize make-up water requirements.

The concept of the present invention developed from our efforts directedtowards a solution of a substantial water pollution problem that iscaused when a water stream is used to remove ammonium hydrosulfide saltsfrom the effluent equipment train associated with such hydrocarbonconversion processes as hydrorefiniug, hydrocracking, etc., whereinammonia and hydrogen sulfide side products are produced. The originalpurpose for injecting the water stream into the etfiuent train of heattransfer equipment associated with these processes was to remove thesedetrimental salts which could clog-up the equipment. The Waste waterstream so-formed presented a substantial pollution hazard insofar as itcontains sulfide salts which have .a substantial biological oxygendemand and ammonia which is a nutrient that leads to excessive growth ofstream vegetation. One solution commonly used in the prior art tocontrol this pollution problem is to strip NH and H 8 from this wastewater stream with resulting recycle of the stripped water to theefliuent equipment. Another solution is to sufliciently dilute the wastewater stream so that the concentration of sulfide salts is reduced to alevel where it is relatively innocuous and to discharge the dilutedstream into a suitable sewer. Our approach to the solution to thisproblem has been diretcted towards a waste water treatment process whichwould :allow recovery of the commercially valuable elemental sulfur andammonia directly from this waste water solution by a controlledoxidation method. However, despite careful and exhaustive investigationsof alternative methods for direct oxidation of the sulfide saltscontained in this waste water stream, we have determined that aninevitable side product of the oxidation step appears to be ammoniumthiosulfate. The presence of ammonium thiosulfate in the treated aqueousstream presents a substantial problem because for etficient control ofthe water pollution problem and in order to have a minimum requirementfor make-up water, it is desired to operate the waste water treatingplant with a closed water loop. That is, it is desired to continuouslyrecycle the treated water stream back to the process in order to removeadditional quantities of the detrimental sulfide salts. The presence ofammonium thiosulfate in this treated aqueous stream prevents the dire-ctrecycling of this stream back to the effiuent equipment associated withthis process primarily because the ammonium thiosulfate. reacts withhydrogen sulfide contained in the efiiuent stream from the process toproduce elemental sulfur, with resulting contamination of thehydrocarbon product stream with free sulfurwhich causes severe corrosionproblems in the downstream equipment. In addition, ammonium thiosulfateis nonvolatile and will contribute to salt formation in the effluentequipment. We have now found a convenient and simple procedure forremoving the ammonium thiosulfate from this treated aqueous streamwithout contaminating the oil stream with free sulfur, and our methodessentially involves passing the treated aqueous stream containingammonium thiosulfate to the hydrocarbon conversion zone, therebyallowing the ammonium thiosulfate to be catalytically reduced tohydrogen sulfide and water within the hydrocarbon conversion process.

It is, accordingly, an object of the present invention to provide acombination process for converting a hydrocarbon charge stock containingsulfurous and nitrogenous contaminants and for simultaneously recoveringsulfur and ammonia. A second object is to eliminate one source of wastewater streams that cause water pollution problems in the vicinity ofpetroleum refineries. A third object is to substantially reduce therequirements for fresh water or makeup water for the operation of ahydrocarbon conversion process wherein hydrogen sulfide and ammonia areproduced as side products. Another object is to provide a combinationprocess wherein a waste water stream containing ammonium hydrosulfide isproduced, wherein this waste water stream is treated to recover sulfurand ammonia to produce a treated aqueous stream, and the treated aqueousstream is recycled to the process to remove additional quantities ofammonia and hydrogen sulfide; that is, to provide a process of this typethat is run in closed loop fashion with regard to the water streamutilized. Still another object is to provide a convenient an simplemethod for treating, in a refinery containing a hydrocracking orhydrorefiin'ng process, a water stream containing ammonium thiosulfateto produce H 8 and H therefrom.

In one embodiment, the present invention is a combination process forconverting a hydrocarbon charge stock containing sulfurous andnitrogenous contaminants and for recovering elemental sulfur and ammoniawhere the requirement for make-up water is minimized. The first step ofthis process involves contacting, in a hydrocarbon conversion zone, thehydrocarbon charge stock, hydrogen and an aqueous recycle streamcontaining (NH S O with a hydrocarbon conversion catalyst at conversionconditions sufficient to form an effluent stream containingsubstantially sulfur-free and nitrogen-free hydrocarbons, hydrogen, NH H8, and H 0. The second step involves cooling and separating the effluentstream from the first step to form a hydrogen-rich gaseous stream, ahydrocarb0n-rich liquid product stream, and an aqueous waste streamcontaining NH HS. The third step involves catalytically treating theaqueous waste stream from the second step With oxygen at oxidizingconditions effective to produce an effluent stream containing elementalsulfur or ammonium polysulfide, NH OH, and (NH S O The fourth stepcomprises separating sulfur and ammonia from the effiuent stream fromthe third step to produce the aqueous recycle stream containing (NH S OAnd, the final step is passing the aqueous stream from the fourth stepto the first step.

In a second embodiment, the process of the present invention encompassesa process as outlined in the first embodiment wherein the hydrocarbonconversion catalyst utilized in the first step comprises a metalliccomponent selected from the metals and compounds of the metals of GroupVIb and Group VIII combined with a refractory inorganic oxide carriermaterial.

In a third embodiment, the present invention is the process describedabove in the first embodiment wherein a water-immiscible sulfur solventis also charged to the third step and wherein the fourth step comprises:separating the effiuent stream from the third step into a sulfur solventphase containing the sulfur formed in said third step and an aqueousphase containing NH OI-I and (NH S O and stripping at least a portion ofthe ammonia from this aqueous phase to produce the aqueous recyclestream containing (NH S O In another embodiment, the process of thepresent invention comprises the process first outlined above wherein thetreating step is operated with less than 0.5 mole of oxygen per mole ofNH HS in the waste stream to produce an aqueous effluent streamcontaining ammonium polysulfide, NH OH and (NH S O and wherein thefourth step comprises: subjecting the aqueous efiluent stream from thethird step to ammonium polysulfide decomposition conditions to produce avapor stream containing NI-I H 8, and H 0, and an aqueous streamcontaining elemental sulfur and (NH S O and separating sulfur from thislast aqueous stream to produce the aqueous recycle stream containing (NHS O In a preferred embodiment, the present invention is a process forconverting a hydrocarbon charge stock containing sulfurous andnitrogenous contaminants and for recovery of elemental sulfur andammonia where the requirement for make-up water is minimized. The firststep of this process involves contacting, in a hydrocarbon con versionzone, the hydrocarbon charge stock, hydrogen and an aqueous recyclestream containing (NH S O with a hydrocarbon conversion catalystcomprising a metallic component selected from the metals and compoundsof the metals of Group VIb and Group VIII combined with a refractoryinorganic oxide material at conversion conditions sufficient to form aneffluent stream containing substantially sulfur-free and nitrogen-freehydrocarbons, hydrogen, NH H 8, and I1 0. The second step involvescooling and separating the efiluent stream from the first step to form ahydrogen-rich gaseous stream, a hydrocarbon-rich liquid product stream,and an aqueous waste stream containing NH HS. The third step comprisescontacting the aqueous waste stream from the second step, and oxygenWith a phthalocyanine catalyst at oxidizing conditions including atemperature less than 200 F. effective to produce an effluent streamcontaining ammonium polysulfide, NH OH, and (NH S O The fourth stepinvolves subjecting the effluent from the third step step to polysulfidedecomposition conditions sufficient to produce a vapor stream containingNH H 8, and H 0 and an aqueous stream containing elemental sulfur and(NI-I S O The fifth step is separating sulfur from the aqueous streamfrom the fourth step to produce the aqueous recycle stream containing(NH S O And, the final step is passing the aqueous recycle stream to thefirst step.

Other objects and embodiments are hereinafter disclosed in the followingdiscussion of the input streams, the output streams and the mechanicsassociated with each of the essential steps of the present invention.

As indicated above, the first steps of the present invention involvesthe catalytic conversion of a hydrocarbon charge stock containingsulfurous and nitrogenous contaminants. The scope of this step isintended to embrace all catalytic petroleum processes which utilizehydrogen in the presence of a hydrocarbon conversion catalyst to reactwith sulfur and nitrogen compounds contained in the charge stock toproduce, inter alia, H 8, and NH Generally, in these processes, thehydrocarbon charge stock containing the sulfurous and nitrogenouscontaminants and hydrogen are passed into contact with a hydrocarbonconversion catalyst comprising a metallic component selected from themetals and compounds of the metals of Group VIb and Group VIII combinedwith a refractory inorganic oxide carrier material at conversionconditions, including an elevated temperature and superatmosphericpressure, sufficient to produce an effluent stream containingsubstantially sulfur-free and nitrogen-free hydrocarbons, hydrogen, H 8and NH One example of a preferred conversion process, included withinthe scope of this first step, is the process known in the art ashydrorefining, or hydrodesulfurization. The principal purpose of ahydrorefining process is to desulfurize a hydrocarbon charge stockcharged thereto by a mild treatment with hydrogen which generally isselective enough to saturate olefinic-type hydrocarbons and to rupturecarbon-nitrogen and carbon-sulfur bonds but is not severe enough tosaturate aromatics. The charge to the hydrorefining process is typicallya charge stock boiling in the range of about 100 F. to about 0 R, suchas a gasoline boiling range charge stock or a kerosine boiling rangecharge stock or a heavy naphtha, which charge stock contains minoramounts of sulfurous and nitrogenous contaminants which are to beremoved without causing any substantial amount of cracking orhydrocracking. The hydrorefining catalyst utilized is preferablydisposed as a fixed bed in the conversion zone and typically comprises ametallic component selected from the transition metals and compounds ofthe transition metals of the Periodic Table. In particular, a preferredhydrorefining catalyst comprises an oxide or sulfide of a Group VIIImetal, especially an iron group metal, mixed with an oxide or sulfide ofa Group VIb metal, especially molybdenum or tungsten. These metalliccomponents are preferably combined with a carrier material whichgenerally is characterized as a refractory inorganic oxide such asalumina, silica, zirconia, titania, etc. Mixtures of these refractoryinorganic oxides are generally also utilized, especially mixtures ofalumina and silica. Moreover, the carrier materials may be syntheticallyprepared or naturally occurring materials such as clays, bauxite, etc.Preferably, the carrier material is not made highly acidic. A preferredhydrorefining catalyst comprises cobalt oxide or sulfide and molybdenumoxide or sulfide combined with an alumina carrier material containing aminor amount of silica. Suitable conditions utilized in this first stepin the hydrorefining mode are: a temperature in the range of about 700to about 900 F., a pressure of about 100 to about 3000 p.s.i.g., aliquid hourly space velocity of about 1 to about 20 hr.- and a hydrogento oil ratio of about 500:1 to about 10,00021 standard cubic feet ofhydrogen per barrel of charge stock.

Another example of the type of conversion process which is preferablyutilized as the first step of the present invention is a hydrocrackingprocess. The principal objective of this type of process is not only toeffect hydrogenation of the charge stock but also to effect selectivecracking or hydrocracking. In general, the hydrocarbon charge stock whenthe first step is hydrocracking is a stock boiling above the gasolinerange such as straight-run gas oil fractions, lubricating oil, coker gasoils, cycle oils, slurry oils, heavy recycle stocks, crude petroleumoils, reduced and/or topped crude oils, etc. Furthermore, thesehydrocarbon charge stocks contain minor amounts of sulfurous andnitrogenous contaminants which may range from about 100 p.p.m. sulfur to3 or 4 wt. percent sulfur or more; typically, the nitrogen concentrationin this charge stock will be substantially less than the sulfurconcentration except for some rare charge stocks, such as those derivedfrom some types of shale oil, which contain more nitrogen than sulfur.The hydrocracking catalyst utilized typically comprises a metalliccomponent selected from the metals and compounds of metals of Group Vlband Group VIII combined with a refractory inorganic oxide. Particularlypreferred metallic components comprise the oxides or sulfides ofmolybdenum and tungsten from Group VII? and iron, cobalt, nickel,platinum and palladium from Group VIII. The preferred refractoryinorganic oxide carrier material is a composite of alumina and silica,although any of the refractory inorganic oxides mentioned hereinbeforemay be utilized as a carrier material if desired. Since it is desiredthat the catalyst possess a cracking function, the acid activity ofthese carrier materials may be further enhanced by the incorporation ofsmall amounts of acidic materials such as fluorine and/ or chlorine. Inaddition, in some cases it is advantageous to include within the carriermaterial a crystalline aluminosilicate either in the hydrogen form or ina rare earth exhanged form. Preferred aluminosilicates are the Type Xand Type Y forms of faujasite, although any other suitablealuminosilicate either naturally occurring or synthetically prepared maybe utilized if desired. Conditions utilized in the first step which itis operated in the hydrocracking mode include: a temperature of about500 to about 1000 F., a pressure in the range of about 300 to about 5000p.s.i.g., a liquid hourly space velocity of about 0.5 to about 15.0 hr.and a hydrogen to oil ratio of about 100011 to about 20.000 11 standardcubic feet of hydrogen per barrel of oil.

Regardless of the details concerning the exact type of process utilizedin the first step, the effluent stream recovered therefrom containssubstantially sulfur-free and nitrogen-free hydrocarbons, hydrogen, NH H8 and H 0. At least some of the Water contained in this efiluent streammay be produced by the reduction of oxygen-containing compoundscontained in the hydrocarbon charge stock; however, it is an essentialfeature of the present invention that the major portion of the watercontained in this eflluent stream is the result of a recycle aqueousstream being charged to the first step as will be explained hereinbelow.In the second step of the present invention, this effiuent stream iscooled, in any suitable cooling means, and then separated, in anysuitable separating means, into a hydrogen-rich gaseous stream, ahydrocarbon-rich liquid product stream, and a waste water streamcontaining NH HS. As discussed previously, the uniform practice of theprior art has been to inject sufficient water into the efiluent streamfrom the first step upstream of the heat exchange equipment in order towash out ammonium sulfide salts that would be otherwise produced whenthe eflluent is cooled to temperatures below about 200 F. As indicatedhereinbefore, an essential feature of the present invention is that thesource of a major portion of the water necessary to wash out theseammonium sulfide salts is a recycle aqueous stream which is charged tothe first step. During startup of the process of the present invention,and during the course of the process, additional make-up water may beadded to the, effiuent stream from the first step, if desired, on theinfluent side of the heat exchange equipment. The total amount of waterutilized is obviously a pronounced function of the amount of NH and H 8in this efiluent stream; typically it is about 1 to about 20 or moregallons of water per gallons of oil charged to the hydrocarbonconversion step. Irrespective of how the water gets into the eflluentstream, the resulting cooled effiuent stream is typically passed to aseparating zone wherein it separates into a hydrogenrich gaseous phase,a hydrocarbon-rich liquid phase and a waste water phase. Thehydrogen-rich gaseous phase is then withdrawn from this zone, and aportion of it typically recycled to the hydrocarbon conversion zonethrough suitable compression means. The hydrocarbon-rich liquid productphase is typically withdrawn and passed to a suitable product recoverysystem which generally, for the type of hydrocarbon conversion processeswithin the scope of the present invention comprises a suitable train offractionating equipment designed to separate this hydrocarbon-richproduct stream into a series of desired products, some of which may berecycled. The aqueous phase formed in the separating zone is typicallywithdrawn to form an aqueous Waste stream containing ammoniumhydrosulfide (NH HS). This stream. may, in some cases, contain excessamounts of NH relative to the amounts of H 8 adsorbed therein, but veryrarely will contain more H 5 than NH because of the relatively lowsolubility of H 8 in an aqueous solution containing a ratio of dissolvedH S to dissolved NH greater than about 1:1.

The amount of NH HS contained in this waste stream may vary over a widerange up to the solubility limit of the sulfide salt in water.Typically, the amount of NH HS is about 1.0 to about 10.0 wt. percent ofthe waste stream. For example, a typical waste water stream from ahydrocracking plant contains 3.7 wt. percent NH HS.

Following this separation step, the aqueous Waste stream producedtherein is passed to a treating step wherein it is catalytically treatedwith oxygen at oxidizing conditions selected to produce an aqueouseffiuent stream containing elemental sulfur or ammonium polysulfide, NHOH and (NH S O In some cases, it is advantageous to remove dissolved orentrained oil contained in this waste stream prior to passing it to thetreatment step; however, in most cases this waste sream is chargeddirecly to the treating step.

The catalyst utilized in the treating step is a suitable solid oxidizingcatalyst that is capable of effecting sub stantially complete conversionof the ammonium hydrosulfide salt contained in this waste stream. Twoparticularly preferred classes of catalyst for this step are metallicsulfides, particularly iron group metallic sulfides, and metalphthalocyanines. The metallic sulfide catalyst is selected from thegroup consisting of sulfides of nickel, cobalt, and iron, with nickelbeing especially preferred. Although it is possible to perform this stepwith a slurry of the metallic sulfide, it is preferred that the metallicsulfide be composited with a suitable carrier material. Examples ofsuitable carrier materials are: charcoal, such as wood charcoal, bonecharcoal, etc., which may or may not be activated prior to use; andrefractory inorganic oxides such as alumina, silica, zirconia,kieselghur, bauxite, etc. and other natural or synthetic highly porousinorganic carrier materials. The preferred carrier materials are aluminaand activated charcoal and thus a preferred catalyst is nickel sulfidecombined with alumina or activated charcoal.

Another preferred catalyst for use in this treatment step is a metalphthalocyanine catalyst combined with a suitable carrier material.Particularly preferred metal phthalocyanine compounds include those ofcobalt and vanadium. Other metal phthalocyanine compounds that may beused include those of iron, nickel, copper, molybdenum, manganese,tungsten, and the like. Moreover, any suitable derivative of the metalphthalocyanine may be employed including the sulfonated derivatives andthe carboxylated derivatives. Any of the carrier materials previouslymentioned in connection with the metallic sulfide catalyst can beutilized with the phthalocyanine catalyst; however, the preferredcarrier material is activated carbon. Hence, a particularly preferredcatalyst for use in the treatment step comprises a cobalt or vanadiumphthalocyanine sulfonate combined with an activated carbon carriermaterial. Additional details as to alternative carrier materials,methods of preparation, and the preferred amounts of catalyticcomponents are given in the teachings of US. Pat. No. 3,108,081 forthese phthalocyanine catalysts.

Although this treatment step can be performed according to any of themethods taught in the art for contacting a liquid stream with a solidcatalyst, the preferred system involves a fixed bed of the solidoxidizing catalyst disposed in a treatment zone. The aqueous wastestream is then passed therethrough in either upward, radial, or downwardflow and the oxygen stream is passed thereto in either concurrent orcountercurrent fiow relative to the aqueous waste stream. Because one ofthe products of this treatment step is elemental sulfur, there is asubstantial catalyst contamination problem caused by the deposition ofthis elemental sulfur on the fixed bed of the catalyst. In general, inorder to avoid sulfur deposition on the catalyst, we prefer to operatethis step in either of two alternative modes. In the first mode, asulfur solvent is admixed with the Waste stream and charged to thetreatment zone in order to effect removal of deposited sulfur from thesolid catalyst. Any suitable sulfur solvent may be utilized providedthat it is substantially inert to the conditions utilized in thetreatment zone and that it dissolves substantial quantities of sulfur.Examples of suitable sulfur solvents are: disulfide compounds such ascarbon disulfide, methyldisulfide, ethyldisulfide, etc.; aromatic compounds such as benzene, toluene, xylene, ethylbenzene, etc.; aliphaticparaffins such as pentane, hexane, heptane, etc.; cyclic parafiins suchas methylcyclopentane, cyclopentanes, cyclohexane, etc.; halidecompounds such as carbon tetrachloride, methylene chloride, ethylenechloride, chloroform, tetrachloroethane, butyl chloride, propyl bromide,ethyldibromide, chlorobenzene, dichlorobenzene, etc.; and the likesolvents. Moreover, mixtures of these solvents may be utilized ifdesired, and in particular a solvent which is particularly effective isan aromatic-rich reformate. In this mode, the preferred operationencompasses the utilization of a sulfur solvent that is substantiallyimmiscible with the aqueous waste stream. Furthermore, the solubility ofsulfur in the solvent is preferably such that it is markedly greater ata temperature in the range of about 175 F. to about 400 F. than it is intemperatures in the range of about 32 F. to about 170 F. This lastpreference facilitates removal of sulfur through crystallization if suchis desired. Considering all of these requirements, we have found thatone preferred sulfur solvent is selected from the group consisting ofbenzene, toluene, xylene, and mixtures thereof. Another group ofpreferred sulfur solvents are the halogenated hydrocarbons.

The amount of sulfur solvent utilized in this treatment step is afunction of the net sulfur production for the particular waste stream,the activity and selectivity characteristics of the catalyst selected,and the solubility characteristics of the sulfur solvent. In general,the volumetric ratio of sulfur solvent to aqueous waste stream isselected such that there is at least enough sulfur solvent to carry awaythe net sulfur production from the oxidation reaction. As a practicalmatter, we have found it convenient to operate at a volumetric ratiosubstantially in excess of the minimum amount required to strip thesulfur from the catalyst; for example, four aqueous waste streamscontaining about 3 wt. percent ammonium hydrosulfide, we have found thata volumetric ratio of about 1 volume of sulfur solvent per volume ofWaste stream gives excellent results. The exact selection of thevolumetic ratio for the particular waste stream and catalyst utilizedcan "be made by a suitable experiment or series of experiments, thedetails of which would be self-evident to one skilled in the art.

Accordingly, in the first mode of operation of the treatment step, asulfur solvent and oxygen are charged in admixture with the aqueouswaste stream to the treatment zone to produce an efiiuent streamcomprising the sulfur solvent containing dissolved sulfur formed by theoxidation reaction, and water containing NH OH,

and, possibly, a minor amount of other oxides of sulfur. This effluentstream is passed to a separating zone where, in the preferred operationin which an immiscible sulfur solvent is utilized, a sulfur solventphase separating from a treated aqueous phase containing NH OH and Atleast a portion of the sulfur solvent phase is then withdrawn from theseparating zone and passed to a suitable sulfur recovery zone wherein atleast a portion of the dissolved sulfur is removed therefrom by any ofthe methods known in the art such as crystallization, distillation, etc.A preferred precedure is to distill off sulfur solvent and recover aslurry of molten sulfur from the bottoms of the sulfur recovery zone.The lean sulfur solvent so-produced can then be recycled to thetreatment step. It is, of course, understood that it is not necessary totreat all of the sulfur solvent to remove sulfur therefrom; that is, itis only necessary to treat an amount of the rich sulfur solventsufiicient to recover the net sulfur production. In any event, anaqueous phase containing NH OH and (NH S O is withdrawn from thisseparating zone, and passed to a stripping zone wherein at least aportion of the ammonia contained therein is removed to produce anaqueous recycle stream containing (NH.,) 8 0 In accordance with thepresent invention, this last stream is passed back to the hydrocarbonconversion step in order to reduce the minor amount of ammoniumthiosulfate contained therein to hydrogen sulfide and water.

The second mode of operation of the treatment step comprises carefullyregulating the stoichiometric amount of oxygen injected into thetreatment zone so that oxygen is provided in an amount less than thestoichiometric amount required to oxidize all of the ammoniumhydrosulfide in the aqueous waste stream to elemental sulfur. Hence, forthis mode it is required that oxygen be present in a mole ratio lessthan 0.50 mole of 0 mole of NH HS and preferably about 0.25 to about0.45 mole of oxygen per mole of ammonium hydrosulfide in the aqueouswaste stream. The exact value within this range is selected such thatsufficient sulfide remains available to react with the net sulfideproductionthat is to say, this mode of operation requires thatsufficient excess sulfide be available to form polysulfide with theelemental sulfur which is the product of the primary oxidation reaction.Since one mole of sulfide will react with many moles of sulfur (i.e.,about 5 moles of sulfur per mole of sulfide), it is generally onlynecessary that a small amount of sulfide remain unoxidized.

In this second mode, an aqueous effluent stream containing ammoniumpolysulfide (NH S O NH OH and a. minor amount of other oxides of sulfuris withdrawn from the treatment step and passed to a polysulfidedecomposition zone whcreiu the polysulfide compound decomposes to yielda vapor stream containing NH H 8 and H 0 and an aqueous streamcontaining elemental sulfur and (NH S O The preferred method fordecomposing the polysulfide solution involves subjecting it toconditions, including a temperature in the range of about 100 F. toabout 350 F. sufficient to form an overhead stream comprising NH H and H0 and a bottom stream comprising elemental sulfur in admixture with anaqueous stream containing (NH S O In most cases, it is advantageous toaccelerate the polysulfide decomposition reaction by stripping H S fromthe polysulfide solution with the aid of a suitable inert gas such assteam, air, flue gas, etc., which can be injected into the bottom of thedecomposition zone. When the bottom stream contains a slurry of sulfur,it is then subjected to any of the techniques taught in the art forremoving a solid from a liquid such as filtration, settling,centrifuging, etc., to remove the elemental sulfur therefrom. In somecases, this bottom stream will contain molten sulfur which can beseparated by a suitable settling step. The resulting aqueous streamseparated from the sulfur contains a minor amount of (NI-19 8 0 and inaccordance with the present invention is recycled to the hydrocarbonconversion step. In the case where the bottom temperature of thedecomposition zone is maintained above 250 F., the separation ofelemental sulfur from the aqueous recycle stream can be performed, ifdesired, within the decomposition zone by allowing a liquid sulfur phaseto form at the bottom of this zone, and separately drawing off theaqueous stream and a liquid sulfur stream.

An essential reactant for both modes of the treatment step is oxygen.This may be present in any suitable form either by itself or mixed withother inert gases. In general, it is preferred to utilize air to supplythe necessary oxygen. As indicated hereinbefore in the second mode theamount of oxygen utilized is less than the stoichiometric amountrequired to oxidize all of the ammonium hydrosulfide to elementalsulfur, and in the first mode of operation, wherein a sulfur solvent isutilized, the amount of oxygen is ordinarily chosen to be slightlygreater than the stoichiometric amount necessary to oxidize all sulfideto sulfur; that is, oxygen is generally utilized in the first mode in amole ratio of about 0.5 :1 to about 1.5 :1 or more moles of oxygen permole of ammonium hydrosulfide contained in the aqueous waste stream.

Regarding the conditions utilized in the treatment step of the presentinvention, it is preferred for both preferred modes of operation toutilize a temperature in the range of about 30 F. up to about 400 F.with a temperature of about 80 F. to about 220 F. yielding best results.In fact, it is especially preferred to operate with a temperature lessthan 200 F., since this minimizes sulfate formation. The sulfideoxidation reaction is not too sensitive to pressure and, accordingly,any pressure which maim tains the Waste stream in the liquid phase maybe utilized. In general, it is preferred to operate at superatmosphericpressure in order to facilitate contact :between the oxygen and theWaste stream, and pressures of about 25 p.s.i.g. to about 75 p.s.i.g. isparticularly preferred. Additionally, the liquid hourly space velocity(defined to be the volume rate per hour of charging the aqueous wastestream divided by the total volume of the treatment zone containingcatalyst) is. preferably selected from the range of about 0:5 to about10.0 hf.

Having broadly characterized the essential steps comprising the processof the present invention, reference is now had to the attached drawingfor a detailed explanation of an example of a preferred flow schemeemployed in the present invention. The attached drawing is merelyintended as a general representation of the flow scheme employed with nointent to give details about heaters, condensers, pumps, compressors,valves, process control equipment, etc. except where a knowledge ofthese devices is essential to an understanding of the present inventionor would not be self-evident to one skilled in. the art. In addition, inorder to provide a working example of a preferred mode of the presentinvention, the attached drawing is discussed with reference to aparticularly preferred mode of operation of each of the steps of thepres- 10 cut invention and preferred catalyst for use in these steps.Moreover, it is to be understood that the description given inconjunction with a discussion of the attached drawing refers to acombination process that has been started up and is producing a treatedaqueous stream which is being recycled to the hydrocarbon conversionstep.

Referring now to the attached drawing, a light gas oil enters thecombination process through line 1. This light gas oil is commingledwith a cycle stock at the junction of line 11 and line 1, with anaqueous recycle waste stream at the junction of line 21 with line 1, andwith a recycle hydrogen stream at the junction of line 7 with line 1.The resulting mixture is then heated via a suitable heating means (notshown) to the desired conversion temperature and then passed intohydrocarbon conversion zone 2. An analysis of the light gas oil shows itto have the following properties; an API gravity at 60 F. of 25, aninitial boiling point of 421 F., a 50% boiling point of 518 F., and anend boiling point of 663 F., a sulfur content of 2.21 wt. percent, and anitrogen content of 126 wt. p.p.m. Hydrogen is supplied via line 7 at arate corresponding to a hydrogen recycle ratio of 10,000 standard cubicfeet of hydrogen per barrel of oil charged to hydrocarbon conversionzone 2. The cycle stock which is being recycled via line 11 is a portionof the 400+ fraction of the product stream which is separated in productrecovery system 10 as will be hereinafter explained. The catalystutilized in zone 2 comprises nickel sulfide combined with a carriermaterial containing silica and alumina in a weight ratio of about 3parts silica per part of alumina. The nickel sulfide is present inamounts sufficient to provide about 5.0 wt. percent nickel in the finalcatalyst. The catalyst is maintained within zone 2 as a fixed bed of /sinch by inch cylindrical pills. The conditions utilized in zone 2 arehydrocracking conditions which include a pressure of about 1500p.s.i.g., a conversion temperature of about 600 F, and a liquid hourlyspace velocity of about 2.0 based on combined feed. An efiluent streamis then withdrawn from zone 2 commingled with a water stream at thejunction of line 9 with line 3 and passed into cooling means 4 whereinthe stream is cooled to a temperature of about F. The cooled mixture isthen passed via line 5 into separating Zone 6 which is maintained at atemperature of about 100 F. and a pressure of about 1450 p.s.i.g. Theamount of water injected into line 3 via line 9 plus the amount addedvia line 21 to the effluent to zone 2 is about 5 gallons of water per100 gallons of oil. As explained hereinbefore, the reason for adding thewater on the influent side of condenser 4 is to insure that thiscondenser does not become clogged with sulfide salts.

In separating zone 6, a three-phase system is formed. The gaseous phasecomprises hydrogen, hydrogen sulfide and a minor amount of light ends.The oil phase contains a relatively large amount of dissolved H S. Thewater phase contains about 5 wt. percent ammonium hydrosulfide with aslight excess of ammonia. The hydrogenrich gaseous phase is withdrawnvia line 7 and a portion of it (about 20 vol. percent) is vented fromthe system via line 13 in order to prevent build-up of excessive amountsof H 8 in this stream. The remainder of the hydrogen stream is passedvia line 7 through compressive means, not shown, and is commingled withadditional make-up hydrogen entering the process via line 23 and passedback to hydrocarbon conversion zone 2. The oil phase from separatingzone 6 is withdrawn via line 8 and passed to product recovery system 10.

In this case, product recovery system 10 comprises a low pressureseparating zone and a suitable train of fractionating means. In the lowpressure separating zone, the product stream is maintained at a pressureof about 100 p.s.i.g. and a temperature of about 100 F. in order tostrip out dissolved H S from this oil stream. The resulting stripped oilstream is fractionated to recover a gasoline boiling range productstream and a cycle oil comprising the portion of the product streamboiling above 400 F. The gasoline product stream is recovered via line12 and the cycle oil is recycled to hydrocarbon conversion zone 2 vialine 11.

Returning to the aqueous phase formed in separating zone 6, it isWithdrawn via line 9 and continuously recycled back to line 3.Additional make-up water is injected through line 14 during start-up ofthe process and to make up to losses during the course of the process.It is a feature of the present invention that the requirement formake-up water is minimized. A drag stream is withdrawn from the waterstream flowing through line 9 at the junction of line 9 with line 15.This drag stream is passed via line 15 to line 16 where it is commingledwith an air stream and, the resulting mixture is passed into treatmentzone 17.

Treatment zone 17 contains a fixed bed of a solid catalyst comprisingcobalt phthalocyanine mono-sulfonate combined with an activated carboncarrier material in an amount such that the catalyst contains 0.5 wt.percent phthalocyanine catalyst. The activated carbon granules used asthe carrier material are in a size of 30-40 mesh. As indicatedhereinbefore, the ammonium hydrosulfide is present in the aqueous wastestream withdrawn from separating zone 6 in an amount of about wt.percent and is charged to treatment zone 17 at a liquid hourly spacevelocity of about 1.0 hr. The amount of air which is also charged totreatment zone 17 via line 16 is about 0.7 atom of oxygen per atom ofsulfide contained in the Waste water stream. As previously explained,this is an amount less than the stoichiometric amount necessary toconvert the sulfide to sulfur, and consequently ammonium polysulfide isformed within treatment zone 17. The conditions utilized in this zoneare a temperature of 95 F. and a pressure of 50 p.s.i.g. Because of sidereactions, a minor amount of the sulfide contained in the aqueous wastestream is oxidized to higher oxides of sulfur, principally (NHQ S ODepending somewhat upon the life of the catalyst utilized within zone17, about 1 to about of the sulfide Will be oxidized to (NH S OAccordingly, the efiluent stream withdrawn from zone 17 via line 18contains ammonium polysulfide, NH OH, (NH S O and a minor amount ofnitrogen gas. This stream is passed to separating system 19 which inthis case comprises: a gas separator, a polysulfide decomposition zoneand a sulfur recovery zone. In the gas separator, the minor amount ofnitrogen gas contained in the effluent stream from treatment zone 17 isvented from the system. In the polysulfide decomposition zone, theliquid effluent stream from the gas separator is heated to a temperatureof about 210 F. and passed into a distillation column wherein anoverhead stream containing NH a minor amount of H 8 and H 0 is recoveredvia line 20 and a bottom stream containing a slurry of elemental sulfurin an aqueous solution of (NH S O is withdrawn as a bottom stream. Thisbottom stream is passed to a sulfur recovery zone wherein the elementalsulfur is filtered from this stream and recovered via line 22. Theresulting elemental sulfur-free aqueous stream containing a minor amountof (NH S O is withdrawn from separating system 19 via line 21 and, inaccordance with the present invention, recycled to hydrocarbonconversion zone 2. Within hydrocarbon conversion zone 2, the ammoniumthiosulfate contained in this aqueous stream is reduced to hydrogensulfide and water. Operations as indicated are continued for ahydrocracking catalyst life of about 20 barrels per pound of catalystand the product stream recovered via line 12 remains substantially freeof elemental sulfur and there is no significant aqueous waste streamdisposal problems. Therefore, a waste water disposal pollution problemhas been abated, elemental sulfur has been recovered from the wastestream, and the loop is closed with respect to recycle water.

We claim as our invention:

1. A process for converting a hydrocarbon charge stock containingsulfurous and nitrogenous contaminants and for simultaneously recoveringelemental sulfur and ammonia, said process comprising the steps of: (a)contacting, in a hydrocarbon conversion zone, the hydrocarbon chargestock, hydrogen, and an aqueous recycle stream containing (NH4)2S2O3with a hydrocarbon conversion catalyst at conversion conditionssufficient to form an efiiuent stream containing substantiallysulfur-free and and nitrogen-free hydrocarbons, hydrogen, NH H 5, and H0; (b) cooling and separating the effluent from step (a) to form ahydrogen-rich gaseous stream, a hydrocarbon-rich liquid product stream,and an aqueous waste stream containing NH HS; (c) catalytically treatingthe aqueous waste stream from step (b) with oxygen at oxidizingconditions etfective to produce an effluent stream containing elementalsulfur or ammonium polysulfide, NH OH, and (NH S O (d) separating sulfurand ammonia from the efiluent stream from step (c) to produce theaqueous recycle stream containing (NH S O and, (e) passing the recyclestream to step (a).

2. The process of claim 1 wherein said hydrocarbon conversion catalystcomprises a metallic component selected from the metals and compounds ofthe metals of Group VIb or Group VIII combined with a refractoryinorganic oxide carrier material.

3. The process of claim 2 wherein said hydrocarbon charge stock boilsabove the gasoline range and said conversion conditions arehydrocracking conditions.

4. The process of claim 2 wherein said hydrocarbon charge stock boils inthe range of about F. to about 650 F. and wherein said conversionconditions are hydrorefining conditions.

5. The process of claim 1 wherein step (c) comprises contacting theaqueous waste stream and oxygen with a phthalocyanine catalyst atoxidizing conditions.

6. The process of claim 1 wherein step (c) comprises contacting theaqueous waste stream and oxygen with a catalyst comprising an iron groupmetallic component combined with a refractory inorganic oxide atoxidizing conditions.

7. The process of claim 1 wherein a water-immiscible sulfur solvent isalso charged to step (c) and wherein step ((1) comprises: separating theeffluent stream from step (c) into a sulfur solvent phase containingsulfur formed in step (c) and an aqueous phase containing N OH and (NH SO and stripping at least a portion of the ammonia from this last aqueousphase to produce the aqueous recycle stream.

8. The process of claim 1 wherein step (c) is operated with less than0.5 mole of oxygen per mole of NH HS in the waste stream to produce anaqueous efiiuent stream containing ammonium polysulfide, NH OH, and

and wherein step (d) comprises: subjecting the effluent stream from step(c) to polysulfide decomposition conditions effective to produce a vaporstream containing NH H 8 and H 0 and an aqueous stream containingelemental sulfur and (NH S O and separating sulfur from this last streamto form said recycle water stream.

9. The process of claim 1 wherein said oxidizing conditions include atemperature less than about 200 F.

10. A process for converting a hydrocarbon charge stock containingsulfurous and nitrogenous contaminants and for simultaneously recoveringelemental sulfur and ammonia, said process comprising the steps of: (a)contacting, in a hydrocarbon conversion zone the hydrocarbon chargestock, hydrogen and an aqueous recycle stream containing (NH S O with ahydrocarbon conversion catalyst at conversion conditions sufficient toform an effluent stream containing substantially sulfur-free andnitrogen-free hydrocarbons, hydrogen, NH H 5 and H 0; (b) cooling andseparating the effluent stream from step (a) to form a hydrogen-richgaseous stream, a hydrocarbon-rich liquid product stream, an aqueouswaste stream containing NH HS; (c) contacting the aqueous Waste streamfrom step (b) and oxygen With a phthalocyanine catalyst at oxidizingconditions including a temperature less than 200 F., effective toproduce an aqueous efiluent stream containing ammonium polysulfide,

and (NH S O (d) subjecting the etfiuent stream from step (c) topolysulfide decomposition conditions effective to produce a vapor streamcontaining NH H 8 and H and an aqueous stream containing elementalsulfur and (NH S O (e) separating sulfur from the aqueous stream fromstep (d) to form said aqueous recycle stream containing (NH S O and (f)passing the recycle stream to step (a).

11. A process for converting a hydrocarbon charge stock containing asulfurous and nitrogenous contaminant and for simultaneously recoveringelemental sulfur and ammonia, said process comprising the steps of: (a)contacting, in a hydrocarbon conversion zone the hydrocarbon chargestock, hydrogen and an aqueous recycle stream containing (NH S O with ahydrocarbon conversion catalyst comprising a metallic component selectedfrom the metals and compounds of metals of Group VI and Group VIIIcombined with a refractory inorganic oxide at conversion conditionssufiicient to form an eflluent stream containing substantiallysulfur-free and nitrogenfree hydrocarbons, hydrogen, NH H 8, and H 0;(b) cooling and separating the eflluent stream from step (a) to form ahydrogen-rich gaseous: stream, a hydrocarbonrich liquid product stream,and an aqueous Waste stream containing NH HS; (c) contacting the aqueouswaste stream from step (b), oxygen, and a Water-immiscible sulfursolvent with a phthalocyanine catalyst at conditions sufficient toproduce an effluent stream containing elemental sulfur, NH OH, and (NH SO (d) separating the eflluent stream from step (c) into a sulfur solventphase containing sulfur formed in step (c) and an aqueous phasecontaining NH OH and (NH S O (e) stripping at least some ammonia fromthe aqueous phase formed in step (d) to produce the aqueous recyclestream containing (NH S O and, (if) passing the recycle stream to step(a).

References Cited UNITED STATES PATENTS 3,340,182 9/1967 Berkman et a1.208-212 DELBERT E. GANTZ, Primary Examiner A. RIMENS, Assistant ExaminerUS. Cl. X.R. 2082l2, 254

